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Buyer Beware: All Vitamin D Supplements Are Not Created Equal (photo: Google)

According to research released today by Kaiser Permanente, the bottles of vitamin D on drugstore shelves may not contain nearly as much actual active vitamin as they say they do. In fact, some bottles may contain as little as 9% of the vitamin D promised on the label.

A team of researchers led by Erin S. LeBlanc, MD of the Kaiser Permanente Center for Health Research in Portland, Oregon tested 55 bottles of vitamin D3 (the type most often recommended nowadays) from 12 different brands - both over the counter and prescription. What they found was a ridiculous amount of variation: Some samples contained as little as 9 percent vitamin D; others contained as much as 146 percent more than indicated.

What's more, the variation wasn't just from brand to brand and bottle to bottle - different pills from the same bottle actually varied in potency. Rather embarrassingly, the pills from the compounders (meaning prescription D) were almost as variable as the OTC pills, varying from 23% to146% of the expected dose. The study is being published today in a research letter in the Journal of the American Medical Society (JAMA)'s journal JAMA Internal Medicine.

The reason this should matter to you right now? It's flu season, and at the top of experts' lists of best cold and flu prevention strategies is to boost your vitamin D intake. Then there's all the research showing that low levels of vitamin D in the blood are linked to breast cancer, colorectal and other cancers, heart disease, and numerous other serious ills. And of course vitamin D is key to building bone health and preventing osteoporosis.

Vitamin D deficiency is much more common than most people think; some studies have found 50 percent of those tested to be D-deficient. A previous study by LeBlanc found that almost 80 percent of women 65 and up were D-deficient, and then found an association between low vitamin D and weight gain.

According to LeBlanc, the best way for consumers to use today's study is to look on the label for the USP verification mark. The U.S. Pharmacopeial Convention (USP) administers a quality verification program for supplements, but it's voluntary, and LeBlanc and her team found that the bottle they tested from a USP verified manufacturer was somewhat more accurate than the other bottles tested. The problem is, the USP program is voluntary, and not many manufacturers participate in it. So many of the most common drugstore brands don't bear the USP label.

According to the study, the most variability was found in pills and capsules containing 1000 ius of vitamin D3, so it might make sense to purchase lower dosage pills (and then take more of them).

Another suggestion is, of course, to try to get your vitamin D the natural way. Here are your options:

1. Enjoy the sunshine. Right now, if you live north of San Francisco on the West Coast or Richmond, Virginia on the East Coast, you're out of luck on this one. But those of you lucky enough to enjoy a more southern exposure should spend 15 minutes in the sun every day without sunscreen. Yep, that's right, skip the sunscreen (except, perhaps, on your nose or face), but just for 15 minutes, no more. The rest of us should work a daily sun soak into our lives starting in April.

2. Drink your milk. In this country, milk is vitamin D-fortified, so this is one guaranteed way to get some D in your diet. Other foods containing vitamin D are listed here.

None of this is to say you should give up on your daily vitamin D supplement. The unofficial RDA for vitamin D as issued by the Institute of Medicine (IOM) in 2010 is 600 ius for those under 70, 800 ius for those over 80. But many health experts (including the Mayo Clinic) recommend at least 1000 ius for those who are D-deficient, and the fact is you may well be one of them.